Several different compounds and combinations thereof have been used in the past as coupling agents for adhering various polymers to glass, especially as protective coatings to prevent abrasion, increase lubricity and to increase alkali resistance of the bond when glass containers so coated are washed. Typical of the types of compounds used are the epoxy reactive silanes shown in U.S. Pat. No. 3,666,539 as well as a mixture of an aminoalkylalkoxysilane and an epoxy resin-methyl methacrylate primer as disclosed in U.S. Pat. No. 3,362,843. As stated in the latter patent, a vinyl resin coating has no natural affinity for glass in that once applied it can be easily peeled therefrom. Thus, the problem of providing an adequate bond between a vinyl coating and glass still exists so that if the protective vinyl envelope around a plastisol coated glass container is accidentally ruptured it will prevent glass fragments from being scattered over a wide area.
Another compound now used as a coupling agent which provides excellent adhesion of vinyl polymers to glass is set forth in U.S. Pat. No. 3,734,763. This compound is N-[beta-(N'-paravinylbenzyl)-aminoethyl]-gamma-aminopropyltrimethoxysilane hydrochloride having the formula ##STR1## The same compound referred to as XZ8-5069 is also described in Applied Polymer Symposium, 19, 75 (1972) as a virtually universal coupling agent and adhesion promoter for almost all plastics to almost all rigid surfaces.
Typical of the mixtures used as coupling agents for various polymers and glass is XZ8-5066 marketed by Dow-Corning Corp., Midland, Michigan which contains 8.4 parts by weight of an epichlorohydrin-bisphenol A resin having an epoxide equivalent of 182 to 189 (commonly known as Epon 820 as described in U.S. Pat. No. 3,666,539, hereby incorporated by reference) and 1.6 parts by weight of N-aminoethyl-gamma-aminopropyltrimethoxysilane (sold by Dow Corning Corp., Midland, Michigan as Z-6020 and by Union Carbide Corp., New York, New York as A-1120) in 45 parts by weight each of ethyleneglycolmonomethyl ether and ethyleneglycolmonoethylether acetate.
Despite the virtues of the coupling agents used in the past, the adhesion obtained between the polymer and glass is still not satisfactory when the coated glass is washed in dilute alkali. It was therefore desirable to develop a more efficacious bond especially for vinyl polymers and glass which would be more alkali resistant, which could be applied economically in a single step and which would render a glass container shatterproof.